Field
Embodiments described generally relate to systems and methods for separating olefinic hydrocarbons.
Description of the Related Art
Olefins are typically produced by converting a hydrocarbon feed at a high temperature to provide a hydrocarbon mixture containing various alkane, alkene, and alkyne hydrocarbons. The hydrocarbon mixture is then fractionated using a series of distillation columns, fractionation columns, compressors, and refrigeration systems to cool, condense, and separate the various hydrocarbon products. Due to the relatively low boiling points of low molecular weight hydrocarbons, ethylene and propylene are frequently employed as refrigerants while separating and fractionating the hydrocarbon mixture.
Many olefin production processes provide a hydrocarbon mixture rich in C2-C4 alkanes and alkenes. The C3 and C4 hydrocarbons can be separated from the hydrocarbon mixture, in part, due to the higher boiling points of C3 and C4 hydrocarbons relative to other compounds in the hydrocarbon mixture. However, the separation of the C2 hydrocarbons into relatively pure (e.g., greater than 95 mol %) ethane and ethylene products requires the use of very low temperature (e.g., about −50° C. to about −140° C.) vapor-liquid flash and fractional distillation processes due to the relatively similar boiling points of ethylene (e.g., about −103.7° C.) and ethane (e.g., about −88.6° C.). Two or more refrigeration systems employing low temperature propylene and ethylene refrigerants are required to separate the methane, hydrogen, and ethylene from ethane. The need for dual refrigerant, low temperature, refrigeration systems requires both significant capital costs and significant operating costs. Further, the low operating temperatures and high operating pressures require the use of special metallurgies and equipment construction imposing additional capital and operating costs.
There is a need, therefore, for improved methods and systems for separating ethane and/or ethylene from a hydrocarbon mixture that in addition to ethane and/or ethylene also includes one or more additional C1 to C20 hydrocarbons.